The present application claims priority to Japanese Application No. P11-162698 filed Jun. 9, 1999 which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to an optical filter for adjusting an amount of light in the visible region, and it particularly relates to a filter for adjusting an amount of light applied to a filter of a variable light amount type for a camera and a video camcorder, which is applied, for example, in a lens system of a camera or a video camcorder as an ND filter (neutral density filter) for adjusting an amount of light on taking pictures. Therefore, it requires a wide range of variation in an amount of light, and it is important that the adjusted light does not suffer from change in color tone.
It has been known that an ND filter (neutral density filter) is used for restricting an amount of light transmitted through a lens system of a camera and a video camcorder.
As described in JP-A-3-35531U and JP-A-5-40294, a conventional ND filter has a fixed density, and a filter is appropriately selected depending on the specification of the system.
The application of the conventional ND filter involves a problem in that continuous change in density cannot be realized. Accordingly, adjustment of an amount of light utilizing electrochromism (EC) is being tried. In a system utilizing EC, electrodes are provided inside two substrates facing each other, and an electric field is applied between the electrodes to deposit silver or tungsten on the surface of the electrode, whereby the amount of light is adjusted.
However, the system utilizing EC involves a problem in that the transmitted light suffers change in wavelength depending on the course of deposition, i.e., the initial stage of deposition, the midstream of deposition and the completion of deposition, and thus neutral light cannot be obtained (as described, for example, in JP-A-10-133236).
Thus, an optical filter for adjusting an amount of light that solves the problem associated with the conventional art is being demanded.
The invention has been completed taking the conventional art into consideration, and an object thereof is to provide a filter for adjusting an amount of light that has a stable constitution realizing change in the amount of light in a wide range without causing a change in a color tone upon a change in the amount of light.
The invention relates to, as a first embodiment, a filter for adjusting an amount of light comprising a liquid crystal cell and a polarizing plate, the liquid crystal cell comprising two transparent substrates each having a transparent electrode facing each other, and a guest-host type liquid crystal filled in a gap between the transparent substrates, and the polarizing plate being loadable and unloadable in a light path incident on the liquid crystal cell.
The invention also relates to, as a second embodiment, a filter for adjusting an amount of light comprising a liquid crystal cell and an optical filter, the liquid crystal cell comprising two transparent substrates each having a transparent electrode facing each other, and a guest-host type liquid crystal filled in a gap between the transparent substrates, and the optical filter being loadable and unloadable in a light path incident on the liquid crystal cell.
In the invention, a combination of at least one polarizing plate or neutral optical filter that can be loaded and unloaded in the light path and a guest-host type liquid crystal cell (a nematic liquid crystal cell or a liquid crystal cell of a phase change type (host) containing a dichroic dye (guest)) fixed on the light path is used, whereby adjustment of an amount of light for change of an amount of incident light can be conducted, and the color tone of the light, the amount of which is adjusted, is slightly changed.